[spark] Stop checking if volume to mount in k8s exists locally (#148)

It's entirely possible (and not an error) to create a podspec that
contains paths to volume-mount that do not exist wherever
service_configuration_lib is being invoked from.

As long as we ensure that we don't double-add things (which is only a
problem due to the way that the env var keys are constructed here),
skipping the existence check should be fine.

service_configuration_lib/spark_config.py

@@ -223,13 +223,12 @@ def _get_k8s_docker_volumes_conf(
 
     for volume in k8s_volumes:
         host_path, container_path, mode = volume['hostPath'], volume['containerPath'], volume['mode']
-        if os.path.exists(host_path) and host_path not in mounted_volumes:
+        if host_path not in mounted_volumes:
             env.update(_get_k8s_volume(host_path, container_path, mode))
             mounted_volumes.add(host_path)
         else:
             log.warning(
-                f'Path {host_path} does not exist on this host or it has already been mounted.'
-                ' Skipping this bindings.',
+                f'Path {host_path} has already been mounted. Skipping this binding.',
             )
     return env
 

tests/spark_config_test.py

@@ -1216,7 +1216,6 @@ def _get_k8s_base_volumes(self):
         """Helper needed to allow tests to pass in github CI checks."""
         return [
             volume for volume in spark_config.K8S_BASE_VOLUMES
-            if os.path.exists(volume['containerPath'])
         ]
 
     @pytest.fixture